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I have gone through your case and can well understand your genuine health concern.
A blocked nose can be from an infection of upper respiratory tract also. If you have a fever and throat pain along with the blocked nose, then it is due to some infection. Allergy also causes blocked nose, sneezing, running nose, dry cough, etc. And yes, allergy is incurable. There is no permanent treatment for allergy as such, but it can be controlled with drugs and other measures.
To control allergy, you should avoid allergens like dust, pollen, specific allergy-causing food, and grasses. Avoid exposure to cold climate and cold beverages. For nasal blockage, you can use some antihistaminic decongestant nasal drops as Nasivion nasal drops. You can also take some oral antiallergic drug like tablet Montek-LC (Montelukast and Levocetirizine) twice daily for ten days if your doctor has not prescribed you an antiallergic medication.